Improved interferometric method for the determination of the mechanical properties of metal oxide films

Most microelectronic devices and sensors are fabricated by using thin film deposition. Understanding metal oxide films is important in the electronic applications. We report an improved interferometric method based on a phase shifting technique to determine the mechanical properties of metal oxide films. Thin films were prepared by ion-beam sputter deposition at low substrate temperature. Quantitative determination of the mechanical properties such as the internal stress, the biaxial elastic modulus and the thermal expansion coefficient were investigated. A phase shifting Twyman-Green interferometer with the phase reduction algorithm was set up to measure the stress in thin films. Two types of circular glass plates, with known Young's moduli, Poisson's ratios and thermal expansion coefficients, were used as coating substrates. The temperatured-dependent stress behavior of the metal oxide films was obtained by heating samples in the range from room temperature to 70 degree C. The stresses of thin films deposited on two different substrates were plotted against the stress measurement temperature, showing a linear dependence. From the slopes of the two lines in the stress versus temperature plot, the intrinsic stress, the biaxial elastic modulus and the thermal expansion coefficient of metal oxide films are then determined.